Wire electrical discharge machining apparatus

ABSTRACT

A machining-energy calculating unit accumulates a discharge current value for each discharge position to calculate a machining energy in a certain time period from the present time to the past time. An energy-distribution changing unit determines the presence or absence of imbalance in the energy by obtaining a machining energy distribution in an up-down direction of the machining gap based on the machining energy, and when there is imbalance, the energy-distribution changing unit produces a new open/close pattern in which a machining energy distribution that eliminates the imbalance. Power feeding is then performed based on the new open/close pattern.

TECHNICAL FIELD

The present invention relates to a wire electrical discharge machiningapparatus.

BACKGROUND ART

In a wire electrical discharge machining apparatus, a wire as oneelectrode is running in an up-down direction and is arranged to beopposed to a workpiece as the other electrode that is controlled to moveon a plane perpendicular to the wire running direction. A pulsedischarge is caused in a machining gap between the wire and theworkpiece (i.e., inter-electrode gap), and the workpiece is machinedinto a desired shape by utilizing heat energy generated due to thedischarge.

In the wire electrical discharge machining apparatus, in a configurationfor supplying power to the inter-electrode gap, the workpiece isdirectly connected to one electrode end of a machining power supply andthe running wire is connected to the other electrode of the machiningpower supply through a feeding point on which the wire is slidable.Generally, two feeding points are provided; one above and the otherbelow the workpiece. In other words, there are two circuits in parallelon upper and lower sides of the workpiece as paths for a dischargecurrent flowing in the wire.

The wire electrical discharge machining apparatus generally employs twomachining power supplies: a sub discharge power supply for inducingspark discharge (pre-discharge) with small current and a main dischargepower supply for supplying large current as a machining current aftergeneration of the spark discharge to perform rough machining and finishmachining.

In the wire electrical discharge machining apparatus, wire breakagesometimes occurs depending upon the machining conditions. If thedischarge is concentrated at one point, the wire electrode is locallyoverheated, which results in wire breakage. Conventionally, varioustechnologies have been proposed for preventing wire breakage bypreventing the local overheating of the wire electrode (for example, seePatent Documents 1 to 3 and the like).

Specifically, a technology is disclosed in Patent Document 1 in whichswitching elements are provided on each current path from a maindischarge power supply to upper and lower side feeding points foropening and closing the current paths individually so that a one-sidefeeding for supplying a main machining current from only one of thefeeding points is performed, and an upper-side feeding only from theupper-side and a lower-side feeding only from the lower side areswitched every predetermined number of continuously applied pulsevoltages. With this technology, large current can be applied withoutoverheating the wire electrode, enabling to prevent wire breakage due tothe heat generation.

In Patent Document 2, a technology is disclosed in which switchingelements are provided on each current path from a main discharge powersupply to upper and lower side feeding points for opening and closingthe current paths individually so that a one-side feeding for supplyinga main machining current from only one of the feeding points isperformed, and an upper-side feeding and a lower-side feeding areswitched asynchronously. With this technology, occurrence of aconcentrated discharge can be prevented, so that breakage of the wireelectrode due to heating can be prevented.

In Patent Document 3, a technology is disclosed in which a device isprovided for measuring a discharge position in an up-down direction in amachining gap based on a difference and a magnitude relation of currentflowing from a sub discharge power supply to an upper-side feeding pointand a lower-side feeding point, and switching elements are provided oneach current path from a main discharge power supply to the upper-sidefeeding point and the lower-side feeding point for opening and closingthe current paths individually. When spark discharge occurs on the upperend side in the machining gap, the upper-side feeding is performed, whenspark discharge occurs on the lower end side in the machining gap, thelower-side feeding is performed, and when spark discharge occurs at thecenter of a workpiece in a thickness direction, anupper-and-lower-both-side feeding for supplying current fromupper-and-lower-both sides simultaneously is performed. The localoverheating of the wire electrode in the center in the up-down directionin the machining gap in which cooling effect tends to be insufficientcan be prevented by switching the feeding system in accordance with thedischarge position.

In a wire electrical discharge machining apparatus, as disclosed inPatent Document 2, machining liquid nozzles are generally provided onthe wire running path between the upper and lower wire guides atpositions that are close in the up-down direction with an opposingposition to the workpiece therebetween, and a wire electrode 1 is cooledand discharge machining swarf is removed by ejecting a high-pressuremachining liquid into the machining gap from upward and downward.

Patent Document 1: Japanese Patent Application Laid-open No. S59-47123

Patent Document 2: Japanese Patent Application Laid-open No. H1-97525

Patent Document 3: Japanese Examined Patent Publication No. H6-61663

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In the upper-and-lower-both-side feeding system, if there is deviationof impedance between two circuits in parallel on upper and lower sidesof the machining gap as paths for a discharge current, it results incausing difference between discharge current values supplied from theupper-side feeding path and the lower-side feeding path to a dischargingposition. Therefore, when concentrated discharge occurs, a wireelectrode is overheated on a side having a larger discharge currentvalue, causing wire breakage more easily. Performing the upper-sidefeeding and the lower-side feeding as disclosed in Patent Documents 1and 2 is effective in preventing wire breakage due to the concentrateddischarge; however, when only one-side feeding is performed, shortcircuit occurs frequently, thereby lowering machining speed.

In the technology disclosed in Patent Document 3, the one-side feedingsystem and the upper-and-lower-both-side feeding system are used incombination, and therefore is considered to enable stable machining bypreventing the frequent short circuit. However, wire breakage is still aproblem because it occurs due to not only the cooling performance of awire electrode by machining liquid but also imbalance in a machiningenergy, that is, locally excessive machining energy by the concentrateddischarge.

In other words, even on the upper and lower end sides of the machininggap where the wire electrode is cooled enough, if imbalance in themachining energy occurs by the concentrated discharge, wire breakageoccurs. It is described in Patent document 3 that overheating of thewire electrode that causes wire breakage is attributed to insufficientcooling in the center in the up-down direction in the machining gap.However, this can be solved by adjusting the amount of the machiningliquid to be ejected. Even when the cooling in the center in the up-downdirection in the machining gap is improved, if there is imbalance in themachining energy, wire breakage occurs in the same way.

The present invention has been achieved in view of the above, and it isan object of the present invention to provide a wire electricaldischarge machining apparatus capable of improving machining speed bypreventing wire breakage due to imbalance in energy that may occur in aninter-electrode gap.

Means for Solving Problem

To achieve the above objects, there is provided a wire electricaldischarge machining apparatus that, when comprising an upper-side paththat passes through an upper-side feeding point on which a wireelectrode is slidable on an upper side of a workpiece and a lower-sidepath that passes through a lower-side feeding point on which the wireelectrode is slidable on a lower side of the workpiece as feeding pathsfor supplying a discharge current from a machining power supply to aninter-electrode gap that is a machining gap between the wire electrodeand the workpiece, includes an upper-side-path open/close unit and alower-side-path open/close unit capable of separately opening andclosing the upper-side path and the lower-side path; an open/closepattern setting unit that performs power feeding in a manner in which aone-side feeding system using either one of the upper-side path and thelower-side path and an upper-and-lower-both-side feeding systemsimultaneously using both of the upper-side path and the lower-side pathare mixed, and sets an open/close pattern for controlling opening andclosing of the upper-side-path open/close unit and the lower-side-pathopen/close unit separately or simultaneously, as an instruction forrealizing a desired feeding mode in each of the one-side feeding systemand the upper-and-lower-both-side feeding system; a discharge positiondetecting unit that detects a discharge position based on any of a subdischarge current value and a main discharge current value supplied fromthe upper-side feeding point and the lower-side feeding point to theinter-electrode gap; a machining energy calculating unit that calculatesa machining energy at a present position of the wire electrode based onthe main discharge current value for every discharge position that isdetected by the discharge position detecting unit in a certain periodfrom a present time to a past time; a machining-energy-distributionchanging unit that, when there is imbalance in machining energydistribution in an up-down direction of the machining gap obtained basedon the machining energy calculated by the machining energy calculatingunit, generates a new open/close pattern in which the machining energydistribution is changed to obtain a predetermined machining energydistribution for eliminating the imbalance; and a driving unit that,upon receiving the new open/close pattern from the machining energydistribution changing unit, performs an open/close control of theupper-side-path open/close unit and the lower-side-path open/close unit,which is to be performed in accordance with an open/close pattern fromthe open/close pattern setting unit, in accordance with the newopen/close pattern.

According to the present invention, in the process of performing a maindischarge by a feeding system mixing an upper-and-lower-both-sidefeeding and two one-side feedings that are formed by individuallyopening and closing path open/close units provided on upper and lowerside feeding paths from a machining power supply to a machining gap(inter-electrode gap) with open/close patterns that are preset in anopen/close pattern setting unit, a machining-energy calculating unitaccumulates a main discharge current value for each discharge positionto calculate a machining energy in a certain time period from thepresent time to the past time, and an energy-distribution changing unitdetermines the presence or absence of imbalance in the energy byobtaining a machining energy distribution in an up-down direction of themachining gap based on the machining energy and, when there is imbalancein the energy, changes to open/close patterns in which a machiningenergy distribution that eliminates the imbalance is obtained forperforming power feeding that eliminates the imbalance. Thus, wirebreakage due to energy imbalance that may occur in the inter-electrodegap can be prevented, and machining speed can be improved.

Effect of the Invention

According to the present invention, wire breakage due to energyimbalance that can occur in an inter-electrode gap can be prevented, andmachining speed can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according toa first embodiment of the present invention.

FIG. 2 is a diagram for explaining a relation between a dischargeposition and a discharge current value at the time of each of powerfeedings of an upper-side feeding and a lower-side feeding.

FIG. 3 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according toa second embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according toa third embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according toa fourth embodiment of the present invention.

EXPLANATIONS OF LETTERS OR NUMERALS

1 wire electrode

2 upper-side wire guide

3 lower-side wire guide

4 workpiece

5 upper feeding point

6 lower feeding point

7 sub-discharge power supply

8 main-discharge power supply

9 upper sub-feeder line

10 upper sub-switching element

11 lower sub-feeder line

12 lower sub-switching element

13 upper main-feeder line

14 upper main-switching element

15 upper main-feeder line

16 lower main-switching element

17, 18 current sensor

19 discharge-position detecting unit

20 machining-energy calculating unit

21 a, 21 b, 21 c, 21 d machining-energy-distribution changing unit

22 a, 22 b feeding-pattern changing unit

23 open/close pattern setting unit

24 oscillator

25 a, 25 b feeding-pulse-energy changing unit

26 reference-machining-energy setting unit

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments of a wire electrical discharge machining apparatusaccording to the present invention will be explained below in detailwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according tothe first embodiment of the present invention. In FIG. 1, referencenumeral 1 denotes a wire electrode. The wire electrode 1 runs, forexample from upward to downward, while being guided by wire guides 2, 3arranged in an up-down direction with an appropriate intervaltherebetween. A plate-shaped workpiece 4 having a certain thickness isarranged on a plane perpendicular to a wire running direction to beopposed to a wire running path between the upper and lower side wireguides 2, 3 with a predetermined machining gap therefrom (hereinafter,“inter-electrode gap”). An upper feeding point 5 is provided at aposition near the upper-side wire guide 2 and a lower feeding point 6 isprovided at a position near the lower-side wire guide 3. The wireelectrode 1 is slidable on the upper and lower feeding points 5, 6.

Machining liquid nozzles, although not shown, are provided on the wirerunning path between the wire guides 2, 3 at positions that are close inthe up-down direction with an opposing position to the workpiece 4therebetween. High-pressure machining liquid is ejected from themachining liquid nozzles into the machining gap from upward anddownward, so that the wire electrode 1 can be cooled and dischargemachining swarf can be removed.

A general configuration of a discharge machining unit is explainedabove. The wire electrical discharge machining apparatus includes asub-discharge power supply 7 and a main-discharge power supply 8 asmachining power supplies for the discharge machining unit. Thesub-discharge power supply 7 mainly generates a voltage pulse of arelatively low voltage for supplying a sub-discharge small current tothe inter-electrode gap for detecting a state of the machining gap(inter-electrode gap) between the wire electrode 1 and the workpiece 4.The main-discharge power supply 8 mainly generates a voltage pulse of apredetermined pulse width at a predetermined voltage level that ishigher than the sub-discharge power supply 7 for supplying amain-discharge large current for machining to the inter-electrode gap.

One electrode end of the sub-discharge power supply 7 is directlyconnected to the workpiece 4. The other electrode end of thesub-discharge power supply 7 is connected to the upper feeding point 5through an upper sub-feeder line 9, and an upper sub-switching element10 is inserted on the upper sub-feeder line 9. At the same time, theother electrode end of the sub-discharge power supply 7 is connected tothe lower feeding point 6 through a lower sub-feeder line 11, and alower sub-switching element 12 is inserted on the lower sub-feeder line11.

One electrode end of the main-discharge power supply 8 is directlyconnected to the workpiece 4. The other electrode end of themain-discharge power supply 8 is connected to the upper feeding point 5through an upper main-feeder line 13, and an upper main-switchingelement 14 is inserted on the upper main-feeder line 13. At the sametime, the other electrode end of the main-discharge power supply 8 isconnected to the lower feeding point 6 through a lower main-feeder line15, and a lower main-switching element 16 is inserted on the lowermain-feeder line 15.

Semiconductor switching elements are used here as the switching elements10, 12, 14, 16; however, relays can also be used in the same manner.

In this manner, there are two circuits in parallel, one on the upperside and the other on the lower side of the workpiece 4, as paths for adischarge current flowing toward the wire electrode 1 from each of thesub-discharge power supply 7 and the main-discharge power supply 8.Moreover, a switching element is provided on each of those current pathsfor opening and closing the path. Therefore, the main discharge currentcan be supplied from the main-discharge power supply 8 while switchingbetween two systems of an upper-and-lower-both-side feeding system usingboth of the upper and lower feeding points and a one-side feeing systemusing either one of the feeding points.

In other words, in the above configuration, when the upper and lowersub-switching elements 10, 12 are simultaneously turned on, the upperand lower sub-feeder lines 9, 11 are closed, and a pulse voltage outputfrom the sub-discharge power supply 7 is applied to the machining gap(inter-electrode gap) between the wire electrode 1 and the workpiece 4through the upper and lower sub-feeder lines 9, 11 and the upper andlower feeding points 5, 6. In response to this, when a sub discharge(pre-discharge) generated in the inter-electrode gap is detected, one orboth of the upper and lower main-switching elements 14, 16 are turnedon, and a pulse voltage output from the main-discharge power supply 8 isapplied to the inter-electrode gap to supply the main discharge currentin either one of the one-side feeding system using the upper-sidefeeding path or the lower-side feeding path and theupper-and-lower-both-side feeding system using both of the upper andlower side feeding paths simultaneously.

Specifically, in the one-side feeding system using the upper-sidefeeding path, when the upper main-switching element 14 is turned on andthe lower main-switching element 16 is turned off, only the uppermain-feeder line 13 is closed, so that the main discharge current issupplied to the inter-electrode gap through the upper main-feeder line13 and the upper feeding point 5.

On the other hand, in the one-side feeding system using the lower-sidefeeding path, when the upper main-switching element 14 is turned off andthe lower main-switching element 16 is turned on, only the lowermain-feeder line 15 is closed, so that the main discharge current issupplied to the inter-electrode gap through the lower main-feeder line15 and the lower feeding point 6.

In the upper-and-lower-both-side feeding system using both of the upperand lower side feeding paths simultaneously, when the upper and lowermain-switching elements 14, 16 are simultaneously turned on, the upperand lower main-feeder lines 13, 15 are closed simultaneously, so thatthe main discharge current is supplied to the inter-electrode gapthrough the upper and lower main-feeder lines 13, 15 and the upper andlower feeding points 5, 6.

The on-off control of the upper and lower sub-switching elements 10, 12and the upper and lower main-switching elements 14, 16 is performed inresponse to a driving signal from an oscillator 24 to be describedbelow. At the time of supplying the main discharge current by performingthe on-off control of the upper and lower main-switching elements 14,16, the on-off control of the upper and lower sub-switching elements 10,12 is performed in conjunction with the corresponding upper and lowermain-switching elements 14, 16 for the purpose thereof. The on-offcontrol of the upper and lower main-switching elements 14, 16 is mainlyexplained.

As described above, the causes of the wire breakage include imbalance ina machining energy, i.e., the machining energy becomes locally excessivedue to occurrence of concentrated discharge, in addition to coolingperformance of the wire electrode by the machining liquid.

Accordingly, in the first embodiment, current sensors 17, 18, adischarge-position detecting unit 19, a machining-energy calculatingunit 20, a machining-energy-distribution changing unit 21 a, anopen/close pattern setting unit 23, and the oscillator 24 are providedso that the main discharge current can be supplied to theinter-electrode gap from the main-discharge power supply 8 by performingthe on-off control of the upper and lower main-switching elements 14, 16to reduce imbalance in the machining energy that may occur in theinter-electrode gap in such power supply configuration. Themachining-energy-distribution changing unit 21 a includes afeeding-pattern changing unit 22 a.

A method of preventing wire breakage by minimizing imbalance in themachining energy caused in the inter-electrode gap is explained byreferring to FIGS. 1 and 2 before explaining configuration and operationof the above. FIG. 2 is a diagram for explaining a relation between adischarge position and a discharge current value at the time of each ofthe one-side feedings of an upper-side feeding and a lower-side feeding.

In the wire electrical discharge machining apparatus, the pulse voltageis first applied from the sub-discharge power supply 7 to an opposinggap (inter-electrode gap) between the wire electrode 1 and the workpiece2 to generate the sub discharge (pre-discharge). Thereafter, a pulsevoltage is subsequently applied to the inter-electrode gap from themain-discharge power supply 8 to supply the main discharge current.

In this case, the main discharge current at the time of the upper-sidefeeding in which only the upper main-switching element 14 is turned onreturns to the main-discharge power supply 8 through the upper feedingpoint 5, the wire electrode 1, the discharge path in the machining gap,and the workpiece 4. In this discharge current path, impedance from themain-discharge power supply 8 to the discharge position increases withan increase in the distance between the discharge position and the upperfeeding point 5. Therefore, as characteristics (a) shown in FIG. 2, themain discharge current at the time of the upper-side feeding is largewhen the discharge position is at the upper end side of the machininggap and is small when the discharge position is at the lower end side ofthe machining gap.

The main discharge current at the time of the lower-side feeding inwhich only the lower main-switching element 16 is turned on returns tothe main-discharge power supply 8 through the lower feeding point 6, thewire electrode 1, the discharge path in the machining gap, and theworkpiece 4. In this discharge current path, impedance from themain-discharge power supply 8 to the discharge position increases withan increase in the distance between the discharge position and the lowerfeeding point 6 contrary to the above. Therefore, as characteristics (b)shown in FIG. 2, the main discharge current at the time of thelower-side feeding is small when the discharge position is at the upperend side of the machining gap and is large when the discharge positionis large at the lower end side of the machining gap.

That is, when the machining energy is large at the upper end side of themachining gap at the time of the upper-side feeding or theupper-and-lower-both-side feeding, the feeding mode is switched to thelower-side feeding, and when the machining energy is small at the lowerend side of the machining gap at the time of the lower-side feeding orthe upper-and-lower-both-side feeding, the feeding mode is switched tothe upper-side feeding. Moreover, each feeding mode on the upper andlower sides is adjusted to reduce a difference in the machining energybetween the upper and lower end sides of the machining gap at the timeof the upper-and-lower-both-side feeding. In this manner, imbalance inthe machining energy can be minimized, enabling to prevent wire breakageand improve machining speed.

Therefore, the open/close pattern setting unit 23 shown in FIG. 1initializes three open/close patterns. The three open/close patternsinclude a pattern that is an instruction for generating a path forcausing a sub discharge by closing the upper and lower sub-feeder lines9, 11 by performing the on-off control of the upper and lowersub-switching elements 10, 12 simultaneously. The three open/closepatterns include two other patterns that are required at the time ofsupplying the main discharge current thereafter. The two other patternsinclude a pattern for closing the upper and lower main-feeder lines 13,15 simultaneously by performing the on-off control of the upper andlower main-switching elements 14, 16 and a pattern for closing one ofthe upper and lower main-feeder lines 13, 15 and opening the other one.When the three open/close patterns are initialized, the timing of theon-off control of the upper and lower main-switching elements 14, 16 andthe number of the on-off controls of the upper and lower main-switchingelements 14, 16 (the number of power feedings) are set in each of thethree open/close patterns so that short circuit does not occurfrequently and machining speed is satisfactory when feeding power fromthe corresponding feeding path.

The open/close pattern setting unit 23 first outputs the open/closepattern that is an instruction for generating a path for causing a subdischarge, and then outputs the above three open/close patterns at thetime of supplying the main discharge current thereafter, to theoscillator 24 to be described below, thereby performing the two one-sidefeeding systems and the upper-and-lower-both-side feeding system mixedat a predetermined ratio.

The current sensor 17 measures the sub discharge current flowing in theupper sub-feeder line 9 at the time of the sub discharge and outputs themeasured value to the discharge-position detecting unit 19. The currentsensor 18 measures the sub discharge current flowing in the lowersub-feeder line 11 at the time of the sub discharge and outputs themeasured value to the discharge-position detecting unit 19 in the samemanner. The current sensors 17, 18 can be provided on the upper andlower main-feeder lines 15, 16 for measuring the main discharge current.

The discharge-position detecting unit 19 calculates a discharge positionby using the value of the current flowing through the upper feedingpoint 5 measured by the current sensor 17 and the value of the currentflowing through the lower feeding point 6 measured by the current sensor18.

The machining-energy calculating unit 20 accumulates the main dischargecurrent value for various discharge positions calculated and detected bythe discharge-position detecting unit 19 during a machining-energyaccumulating time period when the power feeding is performed under thecondition of the open/close patterns set by the open/close patternsetting unit 23 at the time of the main discharge. Moreover, by usingthe accumulated values, the machining-energy calculating unit 20calculates the machining energy at the present machining position of thewire electrode 1 that moves in the up-down direction.

The machining-energy accumulating time period needed for calculating themachining energy is a time interval defining the past time from thepresent time during which the discharge current value is accumulated asthe machining energy. The machining energy can be accumulated in unitsof moving distance of the wire electrode in the up-down direction or thenumber of discharge pulses. The machining energy in a certain timeperiod from the present time to the past time is explained to beobtained by accumulating it with time, however, can be obtained byperforming averaging with, for example, a low pass filter.

The longer or shorter machining-energy accumulating time period makes itimpossible to obtain a correct machining energy distribution at thepresent machining position at the machining-energy-distribution changingunit 21 a. Therefore, the machining-energy accumulating time periodneeds to be set appropriately in the following method.

That is, if the machining-energy accumulating time period is too short,only a small number of discharge pulses can be sampled during that shortperiod, so that appropriate machining energy distribution cannot beobtained. Therefore, the accumulating time period needs to be at least100 μsec considering a general discharge frequency of the wireelectrical discharge machining apparatus and the appropriate number ofdischarge pulses for obtaining the machining energy distribution.

On the other hand, if the accumulating time period is too long, thedischarge current value at a position at which the wire electrode 1 hasalready passed is also accumulated as the machining energy, so that themachining energy cannot be obtained correctly at a moving position ofthe wire electrode 1 in the up-down direction. Thus, the accumulatingtime period needs to be shorter than a time period needed for machiningfor a distance of five times of a diameter of the wire electrode.

The machining-energy-distribution changing unit 21 a memorizes themachining energy in an appropriately predetermined accumulating timeperiod as a target machining energy. If the machining energy in theaccumulating time period is set large, machining speed is improved,however wire breakage easily occurs. In the case of a small machiningenergy, the case will be opposite. Therefore, themachining-energy-distribution changing unit 21 a memorizes the machiningenergy in the accumulating time period to balance machining speed withpossibility of wire breakage as the target machining energy.

Then, the machining-energy-distribution changing unit 21 a obtains themachining energy distribution in the up-down direction in the machininggap in the present power feeding state by the open/close patterns set bythe open/close pattern setting unit 23 based on the machining energycalculated by the machining-energy calculating unit 20, and determinesthe presence or absence of imbalance in the machining energy based on amagnitude relation between the obtained machining energy distributionand the target machining energy. If there is imbalance in the machiningenergy distribution, the machining-energy-distribution changing unit 21a generates new open/close patterns that make it possible to obtain apredetermined machining energy distribution that neutralizes theimbalance, and outputs those new open/close patterns to the oscillator24.

There are two modes for generating the open/close patterns. In the firstmode, open/close patterns are generated in which the machining energydistribution is changed to reduce the difference of the machining energybetween the upper end side and the lower end side in the machining gap.In the second mode, open/close patterns are generated in which themachining energy calculated by the machining-energy calculating unit 20is changed to be close to the target machining energy.

The machining-energy-distribution changing unit 21 a in the firstembodiment includes the feeding-pattern changing unit 22 a as a unit forspecifically realizing the above two modes. In other words, thefeeding-pattern changing unit 22 a realizes the first mode by changingthe open/close patterns set by the open/close pattern setting unit 23into open/close patterns in which the ratio of the number of powerfeedings between from the upper-side path and from the lower-side pathis made different in accordance with the degree of imbalance of thepresent machining energy, and issuing the changed open/close patterns tothe oscillator 24.

Specifically, when the machining energy distribution is smaller than thetarget machining energy, i.e., when there is no imbalance in themachining energy, the feeding-pattern changing unit 22 a generatesopen/close patterns with the same contents as the open/close patternsset by the open/close pattern setting unit 23 and outputs the generatedopen/close patterns to the oscillator 24.

When the machining energy distribution is larger than the targetmachining energy on the upper end side in the machining gap, thefeeding-pattern changing unit 22 a generates open/close patterns inwhich the ratio of the number of the lower-side feedings in theopen/close patterns set by the open/close pattern setting unit 23 ischanged to be higher than a predetermined value and outputs thegenerated open/close patterns to the oscillator 24.

When the machining energy distribution is larger than the targetmachining energy on the lower end side in the machining gap, thefeeding-pattern changing unit 22 a generates open/close patterns inwhich the ratio of the number of the upper-side feedings in theopen/close patterns set by the open/close pattern setting unit 23 ischanged to be higher than a predetermined value and outputs thegenerated open/close patterns to the oscillator 24.

The feeding-pattern changing unit 22 a realizes the second mode in thefollowing manner. That is, the feeding-pattern changing unit 22 achanges the open/close patterns set by the open/close pattern settingunit 23 into open/close patterns in which the ratio of the number ofpower feedings is made different between the one-side feeding using theupper-side path and the one-side feeding using the lower-side path inaccordance with the magnitude of the machining energy calculated byaccumulating the main discharge current values at all dischargepositions during the accumulating time period appropriately set by themachining-energy calculating unit 20, and outputs the changed open/closepatterns to the oscillator 24.

When the power feeding is performed in accordance with the open/closepatterns received from the open/close pattern setting unit 23, if theopen/close patterns received from the feeding-pattern changing unit 22 aare the same as those received from the open/close pattern setting unit23, the oscillator 24 uses the open/close patterns received from theopen/close pattern setting unit 23. In other words, the oscillator 24continues outputting driving signals for performing the on-off controlof the corresponding switching elements the number of power feedings setby using the ratio of the number of power feedings specified for theopen/close patterns received from the open/close pattern setting unit23.

Therefore, when there is no imbalance in the machining energy that maycause wire breakage, in the inter-electrode gap (machining gap), thepower feeding is performed based on the open/close patterns set by theopen/close pattern setting unit 23 in which the two one-side feedingsand the upper-and-lower-both-side feeding are mixed. The open/closepatterns set by the open/close pattern setting unit 23 is such that theratio of the number of power feedings is set high to cause few shortcircuits and be excellent in machining speed. Thus, machining speed canbe improved.

When the power feeding is performed in the above described mixed mode inaccordance with the open/close patterns received from the open/closepattern setting unit 23, if the open/close patterns received from thefeeding-pattern changing unit 22 a are different from those receivedfrom the open/close pattern setting unit 23, the oscillator 24 does notuse the open/close patterns received from the open/close pattern settingunit 23, and outputs driving signals for performing the on-off controlof the switching elements to perform the power feeding in the ratio ofthe number of power feedings specified for the specified feeding path(one of the two one-side feeding paths) in accordance with theopen/close patterns received from the feeding-pattern changing unit 22a.

Accordingly, when there is imbalance in the machining energy that maycause wire breakage, in the inter-electrode gap at the time of one ofthe one-side feedings of the upper-side feeding and the lower-sidefeeding, the power feeding is performed based on the open/close patternsin which the ratio of the number of power feedings is changed high byswitching to the other one-side feeding, enabling to prevent wirebreakage at the time of the one-side feeding.

When the power feeding is performed based on the open/close patternsthat are received from the feeding-pattern changing unit 22 a and thatare changed from those set by the open/close pattern setting unit 23 sothat the ratio of the number of power feedings is made different betweenthe two one-side feedings and the upper-and-lower-both-side feeding inaccordance with the magnitude of the machining energy calculated by themachining-energy calculating unit 20 during the accumulating timeperiod, wire breakage can be prevented and machining speed can beimproved.

According to the first embodiment, the presence or absence of imbalancein the machining energy is determined based on the machining energydistribution obtained from the machining energy in a certain time periodfrom the present time to the past time, and when there is a differencein the machining energy between the upper and lower side feeding pathsto the degree that causes wire breakage, power feeding is performed byswitching the currently performed open/close patterns to those in whichthe ratio of the number of power feedings is changed to reduce themachining energy difference. Thus, wire breakage can be prevented morereliably.

Moreover, the power feeding is performed by switching the currentlyperformed open/close patterns to those in which the ratio of the numberof power feedings is changed to be different between theupper-and-lower-both-side feeding and the two one-side feedings inaccordance with the magnitude of the machining energy in a certainperiod from the present time to the past time. Thus, wire breakage canbe prevented and machining speed can be improved.

Second Embodiment

FIG. 3 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according tothe second embodiment of the present invention. In FIG. 3, thecomponents that are the same or similar to those shown in FIG. 1 (firstembodiment) are denoted by the same reference numerals. The componentspeculiar to the second embodiment are mainly explained below.

In the second embodiment, a method of eliminating imbalance in themachining energy by changing a feeding pulse energy is explained.Specifically, as shown in FIG. 3, the wire electrical dischargemachining apparatus according to the second embodiment includes amachining-energy-distribution changing unit 21 b instead of themachining-energy-distribution changing unit 21 a in the configurationshown in FIG. 1 (first embodiment), and themachining-energy-distribution changing unit 21 b includes afeeding-pulse-energy changing unit 25 a.

A target machining energy with which machining can be performed withless wire breakage at high machining speed is memorized in themachining-energy-distribution changing unit 21 b. Themachining-energy-distribution changing unit 21 b obtains the machiningenergy distribution in the up-down direction in the machining gap in thepresent power feeding state by the open/close patterns set by theopen/close pattern setting unit 23 based on the machining energycalculated by the machining-energy calculating unit 20, and determinesthe presence or absence of imbalance in the machining energy based on amagnitude relation between the obtained machining energy distributionand the target machining energy. If there is imbalance in the machiningenergy distribution, the machining-energy-distribution changing unit 21b generates open/close patterns changed to obtain a predeterminedmachining energy distribution for eliminating the imbalance and outputsthe open/close patterns to the oscillator 24.

There are two modes for generating the open/close patterns. In the firstmode, open/close patterns are generated in which the machining energydistribution is changed to reduce the difference of the machining energybetween the upper end side and the lower end side in a thicknessdirection of the workpiece 4. In the second mode, open/close patternsare generated, in which the machining energy calculated by themachining-energy calculating unit 20 is changed to be close to thetarget machining energy.

The machining-energy-distribution changing unit 21 b in the secondembodiment includes the feeding-pulse-energy changing unit 25 a as aunit for specifically realizing the above two modes. Thefeeding-pulse-energy changing unit 25 a changes the feeding pulse energyper feeding pulse. The method of changing the feeding pulse energyincludes a method of increasing or decreasing a feeding current valueand a method of increasing or decreasing a feeding time length, any ofwhich can be employed. Examples of a specific configuration areexplained below.

Specifically, when employing the method of increasing or decreasing thefeeding current value, a plurality of the upper and lower main-switchingelements 14, 16 is provided respectively in parallel so that the numberof the switching elements that are turned on simultaneously in each ofthe upper and lower sides can be increased or decreased. In this case,the number of the switching elements that are turned on simultaneouslyis determined in accordance with the physical characteristics such asimpedance of the discharge current path. When employing the method ofincreasing or decreasing the feeding time length, because the upper andlower main-switching elements 14, 16 can be controlled to turn on andoff individually, only the on-operation time length of each switchingelement is increased or decreased. The on-operation time length to beincreased or decreased at this case is also determined in accordancewith the physical characteristics such as impedance of the dischargecurrent path.

The feeding-pulse-energy changing unit 25 a realizes the first mode bychanging the open/close patterns set by the open/close pattern settingunit 23 into open/close patterns in which the feeding pulse energy ismade different between for the time of the power feeding from theupper-side path and the power feeding from the lower-side path inaccordance with the degree of imbalance of the present machining energy,and issuing the changed open/close patterns to the oscillator 24.

Specifically, when the machining energy distribution is smaller than thetarget machining energy, i.e., when there is no imbalance in themachining energy, the feeding-pulse-energy changing unit 25 a generatesopen/close patterns with the same contents as the open/close patternsset by the open/close pattern setting unit 23 and outputs the generatedopen/close patterns to the oscillator 24.

When the machining energy distribution is larger than the targetmachining energy on the upper end side of the workpiece 4, thefeeding-pulse-energy changing unit 25 a generates open/close patterns inwhich the feeding pulse energy at the time of the upper-side feeding bythe open/close patterns set by the open/close pattern setting unit 23 ischanged to be smaller than a predetermined value or the feeding pulseenergy at the time of the lower-side feeding by the open/close patternsset by the open/close pattern setting unit 23 is changed to be largerthan a predetermined value, and outputs the generated open/closepatterns to the oscillator 24.

When the machining energy distribution is larger than the targetmachining energy on the lower end side of the workpiece 4, thefeeding-pulse-energy changing unit 25 a generates open/close patterns inwhich the feeding pulse energy at the time of the upper-side feeding bythe open/close patterns set by the open/close pattern setting unit 23 ischanged to be larger than a predetermined value or the feeding pulseenergy at the time of the lower-side feeding by the open/close patternsset by the open/close pattern setting unit 23 is changed to be smallerthan a predetermined value, and outputs the generated open/closepatterns to the oscillator 24.

At the time of the both-upper-and-lower-side feeding by the open/closepatterns set by the open/close pattern setting unit 23, thefeeding-pulse-energy changing unit 25 a can perform the above process ofchanging the feeding pulse energy simultaneously in the upper-sidefeeding and the lower-side feeding.

The feeding-pulse-energy changing unit 25 a realizes the second mode inthe following manner. That is, the feeding-pulse-energy changing unit 25a changes the open/close patterns set by the open/close pattern settingunit 23 into open/close patterns in which the feeding pulse energy ismade different between the two one-side feedings each using one of theupper and lower side paths and the both-upper-and-lower-side feedingusing both of the paths simultaneously in accordance with the magnitudeof the machining energy calculated by accumulating the main dischargecurrent values at all discharge positions during the accumulating timeperiod appropriately set by the machining-energy calculating unit 20,and outputs the changed open/close patterns to the oscillator 24.

When the power feeding is performed in accordance with the open/closepatterns received from the open/close pattern setting unit 23, if theopen/close patterns received from the feeding-pulse-energy changing unit25 a are the same as those received from the open/close pattern settingunit 23, the oscillator 24 uses the open/close patterns received fromthe open/close pattern setting unit 23. In other words, the oscillator24 continues outputting driving signals for performing the on-offcontrol of the corresponding switching elements so that feeding pulseenergy same as the currently performed one is supplied.

Therefore, when there is no imbalance in the machining energy that maycause wire breakage, in the inter-electrode gap, the power feeding isperformed based on the open/close patterns set by the open/close patternsetting unit 23 in which the two one-side feedings and theupper-and-lower-both-side feeding are mixed. When the open/closepatterns set by the open/close pattern setting unit 23 are performed,high feeding pulse energy that causes few short circuits and isexcellent in machining speed can be supplied to the feeding path, sothat machining speed can be improved.

When the power feeding is performed in the above described mixed mode inaccordance with the open/close patterns received from the open/closepattern setting unit 23, if the open/close patterns received from thefeeding-pulse-energy changing unit 25 a are different from thosereceived from the open/close pattern setting unit 23, the oscillator 24does not use the open/close patterns received from the open/closepattern setting unit 23, and outputs driving signals for performing theon-off control of the corresponding switching elements to supply thefeeding pulse energy specified for the specified feeding path (one orboth of the two one-side feeding paths) in accordance with theopen/close patterns received from the feeding-pulse-energy changing unit25 a.

Accordingly, when there is imbalance in the machining energy that maycause wire breakage, in the inter-electrode gap at the time of one ofthe one-side feedings of the upper-side feeding and the lower-sidefeeding, the power feeding is performed based on the open/close patternsin which the feeding pulse energy at the time of the other one-sidefeeding is increased, enabling to prevent wire breakage at the time ofthe one-side feeding and improve machining speed.

When the power feeding is performed based on the open/close patternsthat are received from the feeding-pulse-energy changing unit 25 a andthat are changed from those set by the open/close pattern setting unit23 so that the feeding pulse energy is made different between the twoone-side feedings and the upper-and-lower-both-side feeding inaccordance with the magnitude of machining energy calculated by themachining-energy calculating unit 20 during the accumulating timeperiod, wire breakage can be prevented and machining speed can beimproved.

According to the second embodiment, the presence or absence of imbalancein the machining energy is determined based on the machining energydistribution obtained from the machining energy in a certain period fromthe present time to the past time, and when there is a difference in themachining energy between the upper and lower side feeding paths to thedegree that causes wire breakage, power feeding is performed byswitching the currently performed open/close patterns to those in whichthe feeding pulse energy per feeding pulse is changed to reduce themachining energy difference. Thus, wire breakage can be prevented morereliably.

Moreover, the power feeding is performed by switching the currentlyperformed open/close patterns to those in which the feeding pulse energyper feeding pulse is changed to be different between theupper-and-lower-both-side feeding and the two one-side feedings inaccordance with the magnitude of the machining energy in a certainperiod from the present time to the past time. Thus, wire breakage canbe prevented and machining speed can be improved.

Third Embodiment

FIG. 4 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according tothe third embodiment of the present invention. In FIG. 4, the componentsthat are the same or similar to those shown in FIG. 1 (first embodiment)are denoted by the same reference numerals. The components peculiar tothe third embodiment are mainly explained below.

As shown in FIG. 4, the wire electrical discharge machining apparatusaccording to the third embodiment includes amachining-energy-distribution changing unit 21 c instead of themachining-energy-distribution changing unit 21 a in the configurationshown in FIG. 1 (first embodiment). The machining-energy-distributionchanging unit 21 c includes a reference-machining-pulse-energy settingunit 26 that receives the output from the machining-energy calculatingunit 20 and a feeding-pattern changing unit 22 b that receives theoutput from the reference-machining-pulse-energy setting unit 26, andthe output from the feeding-pattern changing unit 22 b is output to theoscillator 24.

Reference machining pulse energy referred to as an output target of themachining-energy calculating unit 20 is set in thereference-machining-pulse-energy setting unit 26. When receiving themachining energy calculated during the appropriately set accumulatingtime period from the machining-energy calculating unit 20, thereference-machining-pulse-energy setting unit 26 outputs the receivedmachining energy and the corresponding reference machining pulse energyto the feeding-pattern changing unit 22 b.

The feeding-pattern changing unit 22 b generates the open/close patternsin which the ratio of the number of power feedings is changed so thatthe machining energy calculated by the machining-energy calculating unit20 is close to the reference machining energy, and outputs the generatedopen/close patterns to the oscillator 24.

Specifically, the feeding-pattern changing unit 22 b changes theopen/close patterns set by the open/close pattern setting unit 23 tothose in which the ratio of the number of the upper-side feedings is lowin the case where the machining energy calculated by themachining-energy calculating unit 20 is large on the upper end side orsmall on the lower end side in the machining gap with respect to thereference machining energy, and outputs the changed open/close patternsto the oscillator 24.

Moreover, the feeding-pattern changing unit 22 b changes the open/closepatterns set by the open/close pattern setting unit 23 to those in whichthe ratio of the number of the upper-side feedings is high in the casewhere the machining energy calculated by the machining-energycalculating unit 20 is small on the upper end side or large on the lowerend side in the machining gap with respect to the reference machiningenergy, and outputs the changed open/close patterns to the oscillator24.

Furthermore, the feeding-pattern changing unit 22 b changes theopen/close patterns set by the open/close pattern setting unit 23 tothose in which the ratio of the number of the upper-and-lower-both-sidefeedings is low in the case where the machining energy calculated by themachining-energy calculating unit 20 is large on both of the upper andlower end sides in the machining gap with respect to the referencemachining energy, and changes the open/close patterns set by theopen/close pattern setting unit 23 to those in which the ratio of thenumber of the upper-and-lower-both-side feedings is high in the oppositecase where the machining energy calculated by the machining-energycalculating unit 20 is small on both of the upper and lower end sides inthe machining gap. Then, the feeding-pattern changing unit 22 b outputsthe changed open/close patterns to the oscillator 24.

In the first embodiment, a method is explained in which when there isimbalance in the machining energy, the open/close patterns are changedto realize a uniform machining energy distribution on the wire electrodethereby preventing wire breakage.

However, it is preferable in some cases to have a specific nonuniformmachining energy distribution in accordance with the discharge positionsinstead of having a uniform machining energy distribution on the wireelectrode. In the third embodiment, such case can be coped with bysetting the specific nonuniform distribution as the reference machiningenergy in the reference-machining-energy setting unit 26. Two specificapplication examples are explained.

A first application example is explained for a case of preventing wirebreakage that may occur due to wearing of the wire electrode. The wireelectrode 1 is conveyed from the upper side to the lower side of theworkpiece 4. While moving from the upper end side to the lower end sidein the machining gap, the wire electrode 1 wears and becomes thin due todischarging. Particularly, when moving speed of the wire electrode 1 islow or the energy per discharge pulse is large, an amount of wear of thewire electrode 1 increases. Therefore, if the machining energy isuniform when the discharge position is at the upper and lower end sidesin the machining gap, breakage of the wire electrode 1 easily occurs ata position corresponding to the lower end side of the machining gap.

Thus, when the degree of the wire electrode wearing is large, thereference machining energy is set so that the machining energy is smallin the case where the discharge position is on the lower end side in themachining gap compared with the case where the discharge position is onthe upper end side. Accordingly, the machining energy of the thinnedwire electrode 1 due to wearing becomes small at a positioncorresponding to the lower end side in the machining gap, enabling toprevent wire breakage.

A second application example is explained for a case of preventing wirebreakage that may occur when the amount of machining swarf accumulatedin the machining gap is different between the upper and lower end sidesin the machining gap. As described above, the machining liquid nozzlesare provided on the upper and lower sides of the workpiece 4 on an axiscoaxial to the wire electrode 1 in the wire electrical dischargemachining apparatus, and machining liquid is ejected from the machiningliquid nozzles into the machining gap between the wire electrode 1 andthe workpiece 4 to remove machining swarf. The machining liquid flowsinto the machining gap from above and below become different dependingupon the positions at which the machining nozzles are arranged.Machining swarf tends to be accumulated on a side with less machiningliquid flow in the machining gap, which results in high dischargefrequency, so that wire breakage easily occurs on this side.

When the machining liquid flows less on the upper end side in themachining gap, wire breakage easily occurs at a position correspondingto the upper end side in the machining gap. Therefore, when thedischarge position is on the upper end side in the machining gap, thereference machining energy is set so that the machining energy issmaller than the case where the discharge position is on the lower endside.

On the contrary, when the machining liquid flows less on the lower endside in the machining gap, wire breakage easily occurs at a positioncorresponding to the lower end side in the machining gap. Therefore,when the discharge position is on the lower end side in the machininggap, the reference machining energy is set so that the machining energyis smaller than the case where the discharge position is on the upperend side.

Because the amount of the machining liquid flowing into the machininggap respectively from the upper end side and the lower end side isdifferent, the machining energy is small when the wire electrode 1 is ata position corresponding to the upper or lower end side in the machininggap in which less machining liquid flows and the discharge frequency ishigh, enabling to prevent wire breakage.

According to the third embodiment, the reference machining energy ispreset as a target value of the machining energy in a certain periodfrom the present time to the past time, and the power feeding isperformed by switching the currently performed open/close patterns tothose in which the ratio of the number of power feedings is changed toreduce the machining energy difference based on the magnitude relationbetween both energies. Thus, wire breakage can be prevented morereliably.

In addition, wire breakage due to, for example, wearing of the wireelectrode or imbalance of the machining liquid flow in the up-downdirection can be prevented by setting the reference machining energy toprovide a specific nonuniform distribution corresponding to thedischarge position.

Fourth Embodiment

FIG. 5 is a schematic diagram illustrating a configuration of a relevantportion of a wire electrical discharge machining apparatus according tothe fourth embodiment of the present invention. In FIG. 5, thecomponents that are the same or similar to those shown in FIG. 1 (firstembodiment) are denoted by the same reference numerals. The componentspeculiar to the fourth embodiment are mainly explained below.

As shown in FIG. 5, the wire electrical discharge machining apparatusaccording to the fourth embodiment includes amachining-energy-distribution changing unit 21 d instead of themachining-energy-distribution changing unit 21 a in the configurationshown in FIG. 1 (first embodiment). The machining-energy-distributionchanging unit 21 d includes the reference-machining-pulse-energy settingunit 26 that receives the output from the machining-energy calculatingunit 20 and a feeding-pulse-energy changing unit 25 b that receives theoutput from the reference-machining-pulse-energy setting unit 26, andthe output from the feeding-pulse-energy changing unit 25 b is output tothe oscillator 24. Because the reference-machining-pulse-energy settingunit 26 is explained in the third embodiment, the feeding-pulse-energychanging unit 25 b that changes the feeding pulse energy per feedingpulse is explained here. As explained in the second embodiment, themethod of changing the feeding pulse energy includes the method ofincreasing or decreasing a feeding current value and the method ofincreasing or decreasing a feeding time length, any of which can beemployed.

The feeding-pulse-energy changing unit 25 b generates open/closepatterns in which the feeding pulse energy per feeding pulse is changedto be close to the reference machining energy and outputs the generatedopen/close patterns to the oscillator 24.

Specifically, the feeding-pulse-energy changing unit 25 b changes toopen/close patterns in which the feeding pulse energy per feeding pulseis made small at the time of the upper-side feeding in the case wherethe machining energy calculated by the machining-energy calculating unit20 is large on the upper end side in the machining gap with respect tothe reference machining energy, and outputs the changed open/closepatterns to the oscillator 24.

Moreover, the feeding-pulse-energy changing unit 25 b changes toopen/close patterns in which the feeding pulse energy per feeding pulseis made large at the time of the upper-side feeding in the case wherethe machining energy calculated by the machining-energy calculating unit20 is small on the upper end side in the machining gap with respect tothe reference machining energy, and outputs the changed open/closepatterns to the oscillator 24.

Furthermore, the feeding-pulse-energy changing unit 25 b changes toopen/close patterns in which the feeding pulse energy per feeding pulseis made small at the time of the lower-side feeding in the case wherethe machining energy calculated by the machining-energy calculating unit20 is large on the lower end side in the machining gap with respect tothe reference machining energy, and outputs the changed open/closepatterns to the oscillator 24.

Furthermore, the feeding-pulse-energy changing unit 25 b changes toopen/close patterns in which the feeding pulse energy per feeding pulseis made large at the time of the lower-side feeding in the case wherethe machining energy calculated by the machining-energy calculating unit20 is small on the lower end side in the machining gap with respect tothe reference machining energy, and outputs the changed open/closepatterns to the oscillator 24.

Furthermore, the feeding-pulse-energy changing unit 25 b changes toopen/close patterns in which the feeding pulse energy per feeding pulseis made large at the time of the upper-and-lower-both-side feeding inthe case where the machining energy calculated by the machining-energycalculating unit 20 is small on both of the upper and lower end sides inthe machining gap with respect to the reference machining energy, andchanges to open/close patterns in which the feeding pulse energy perfeeding pulse is made small at the time of the upper-and-lower-both-sidefeeding in the case where the machining energy is large on both of theupper and lower end sides in the machining gap. Then, thefeeding-pulse-energy changing unit 25 b outputs the changed open/closepatterns to the oscillator 24.

With this configuration also, the reference machining energy can be setto provide a specific nonuniform distribution corresponding to thedischarge position, so that wire breakage due to wearing of the wireelectrode or imbalance of the amount of the machining liquid flow in theup-down direction can be prevented.

According to the fourth embodiment, the reference machining energy ispreset as a target value of the machining energy in a certain periodfrom the present time to the past time, and the power feeding isperformed by switching the currently performed open/close patterns tothose in which the feeding pulse energy per feeding pulse is changed toreduce the machining energy difference based on the magnitude relationbetween both energies. Thus, wire breakage can be prevented morereliably.

In addition, wire breakage due to, for example, wearing of the wireelectrode or imbalance of the amount of the machining liquid flow in theup-down direction can be prevented by setting the reference machiningenergy to provide a specific nonuniform distribution corresponding tothe discharge position.

In the third and fourth embodiments, each of themachining-energy-distribution changing units 21 c, 21 d includes thereference-machining-pulse-energy setting unit 26, and thefeeding-pattern changing unit 22 b or the feeding-pulse-energy changingunit 25 b, however, can include only thereference-machining-pulse-energy setting unit 26. Even with suchconfiguration, the machining energy distribution can be made close to anoptimal one by generating open/close patterns in which themachining-energy-distribution is changed to reduce the differencebetween the machining energy calculated by the machining-energycalculating unit 20 and the reference machining energy. Therefore, wirebreakage can be prevented. Thus, wire breakage due to wearing of thewire electrode or imbalance of the amount of the machining liquid flowin the up-down direction can be prevented similarly to the above.

INDUSTRIAL APPLICABILITY

As described above, a wire electrical discharge machining apparatusaccording to the present invention is advantageously used to improvemachining speed by preventing wire breakage due to imbalance in themachining energy that occurs in the inter-electrode gap.

1. A wire electrical discharge machining apparatus, when comprising anupper-side path that passes through an upper-side feeding point on whicha wire electrode is slidable on an upper side of a workpiece and alower-side path that passes through a lower-side feeding point on whichthe wire electrode is slidable on a lower side of the workpiece asfeeding paths for supplying a discharge current from a machining powersupply to an inter-electrode gap that is a machining gap between thewire electrode and the workpiece, the wire electrical dischargemachining apparatus comprising: an upper-side-path open/close unit and alower-side-path open/close unit capable of separately opening andclosing the upper-side path and the lower-side path; an open/closepattern setting unit that performs power feeding in a manner in which aone-side feeding system using either one of the upper-side path and thelower-side path and an upper-and-lower-both-side feeding systemsimultaneously using both of the upper-side path and the lower-side pathare mixed, and sets an open/close pattern for controlling opening andclosing of the upper-side-path open/close unit and the lower-side-pathopen/close unit separately or simultaneously, as an instruction forrealizing a desired feeding mode in each of the one-side feeding systemand the upper-and-lower-both-side feeding system; a discharge positiondetecting unit that detects a discharge position based on any of a subdischarge current value and a main discharge current value supplied fromthe upper-side feeding point and the lower-side feeding point to theinter-electrode gap; a machining energy calculating unit that calculatesa machining energy at a present position of the wire electrode based onthe main discharge current value for every discharge position that isdetected by the discharge position detecting unit in a certain periodfrom a present time to a past time; a machining-energy-distributionchanging unit that, when there is imbalance in machining energydistribution in an up-down direction of the machining gap obtained basedon the machining energy calculated by the machining energy calculatingunit, generates a new open/close pattern in which the machining energydistribution is changed to obtain a predetermined machining energydistribution for eliminating the imbalance; and a driving unit that,upon receiving the new open/close pattern from the machining energydistribution changing unit, performs an open/close control of theupper-side-path open/close unit and the lower-side-path open/close unit,which is to be performed in accordance with an open/close pattern fromthe open/close pattern setting unit, in accordance with the newopen/close pattern.
 2. The wire electrical discharge machining apparatusaccording to claim 1, wherein the machining-energy-distribution changingunit, when there is imbalance in the machining energy, generates the newopen/close pattern in which the machining energy distribution is changedto reduce a machining energy difference between an upper end side and alower end side of the machining gap.
 3. The wire electrical dischargemachining apparatus according to claim 1, wherein themachining-energy-distribution changing unit, when there is imbalance inthe machining energy, generates the new open/close pattern in which themachining energy calculated by the machining energy calculating unit ischanged to be close to a preset appropriate machining energy.
 4. Thewire electrical discharge machining apparatus according to claim 1,wherein the machining-energy-distribution changing unit includes afeeding pattern changing unit that changes the open/close pattern set bythe open/close pattern setting unit to the new open/close pattern inwhich a ratio between number of power feedings from the upper-side pathand number of power feedings from the lower-side path is made different,depending upon a magnitude of present imbalance in the machining energy.5. The wire electrical discharge machining apparatus according to claim1, wherein the machining-energy-distribution changing unit includes afeeding pattern changing unit that changes the open/close pattern set bythe open/close pattern changing unit to the new open/close pattern inwhich a ratio of number of power feedings is made different between thetwo one-side feedings and the upper-and-lower-both-side feeding,depending upon a magnitude of the machining energy calculated by themachining energy calculating unit.
 6. The wire electrical dischargemachining apparatus according to claim 1, wherein themachining-energy-distribution changing unit includes afeeding-pulse-energy changing unit that changes the open/close patternset by the open/close pattern setting unit to the new open/close patternin which a feeding pulse energy per feeding pulse is made differentbetween at a time of power feeding using the upper-side path and at atime of power feeding using the lower-side path to cause the machiningenergy calculated by the machining energy calculating unit to be closeto a preset appropriate machining energy, depending upon a magnitude ofpresent imbalance of the machining energy.
 7. The wire electricaldischarge machining apparatus according to claim 1, wherein themachining-energy-distribution changing unit includes afeeding-pulse-energy changing unit that changes the open/close patternset by the open/close pattern setting unit to the new open/close patternin which a feeding pulse energy per feeding pulse is made differentbetween the two one-side feedings and the upper-and-lower-both-sidefeeding, depending upon a magnitude of the machining energy calculatedby the machining energy calculating unit.
 8. The wire electricaldischarge machining apparatus according to claim 1, wherein themachining-energy-distribution changing unit includes areference-machining-energy setting unit that sets a reference machiningenergy that provided a target value for the machining energy to becalculated by the machining energy calculating unit, and generates thenew open/close pattern in which the machining energy distribution ischanged to reduce a difference between the machining energy calculatedby the machining energy calculating unit and the reference machiningenergy.
 9. The wire electrical discharge machining apparatus accordingto claim 1, wherein the machining-energy-distribution changing unitincludes a reference-machining-energy setting unit that sets a referencemachining energy that provides a target value for the machining energyto be calculated by the machining energy calculating unit and provides amachining energy value that is different between an upper end side and alower end side of the machining gap, and generates the new open/closepattern in which the machining energy distribution is changed to reducea difference between the machining energy calculated by the machiningenergy calculating unit and the reference machining energy.
 10. The wireelectrical discharge machining apparatus according to claim 1, whereinthe machining-energy-distribution changing unit includes areference-machining-energy setting unit that sets a reference machiningenergy that provides a target value for the machining energy to becalculated by the machining energy calculating unit; and a feedingpattern changing unit that changes the open/close pattern set by theopen/close pattern setting unit to the new open/close pattern in which aratio of number of power feedings is made different between the twoone-side feedings and the upper-and-lower-both-side feeding to reduce adifference between the machining energy calculated by the machiningenergy calculating unit and the reference machining energy.
 11. The wireelectrical discharge machining apparatus according to claim 1, whereinthe machining-energy-distribution changing unit includes areference-machining-energy setting unit that sets a reference machiningenergy that provides a target value for the machining energy to becalculated by the machining energy calculating unit and provides amachining energy value that is different between an upper end side and alower end side of the machining gap; and a feeding pattern changing unitthat changes the open/close pattern set by the open/close patternsetting unit to the new open/close pattern in which a ratio of number ofpower feedings is made different between the two one-side feedings andthe upper-and-lower-both-side feeding to reduce a difference between themachining energy calculated by the machining energy calculating unit andthe reference machining energy.
 12. The wire electrical dischargemachining apparatus according to claim 1, wherein themachining-energy-distribution changing unit includes areference-machining-energy setting unit that sets a reference machiningenergy that provides a target value for the machining energy to becalculated by the machining energy calculating unit; and a feeding pulseenergy changing unit that changes the open/close pattern set by theopen/close pattern setting unit to the open/close pattern in which afeeding pulse energy per feeding pulse is made different between at atime of power feeding using the upper-side path and at a time of powerfeeding using the lower-side path to reduce a difference between themachining energy calculated by the machining energy calculating unit andthe reference machining energy.
 13. The wire electrical dischargemachining apparatus according to claim 1, wherein themachining-energy-distribution changing unit includes areference-machining-energy setting unit that sets a reference machiningenergy that provides a target value for the machining energy to becalculated by the machining energy calculating unit and provides amachining energy value that is different between an upper end side and alower end side of the machining gap; and a feeding pulse energy changingunit that changes the open/close pattern set by the open/close patternsetting unit to the open/close pattern in which a feeding pulse energyper feeding pulse is made different between at a time of power feedingusing the upper-side path and at a time of power feeding using thelower-side path to reduce a difference between the machining energycalculated by the machining energy calculating unit and the referencemachining energy.
 14. The wire electrical discharge machining apparatusaccording to claim 1, wherein the machining-energy-distribution changingunit includes a reference-machining-energy setting unit that sets areference machining energy that provides a target value for themachining energy to be calculated by the machining energy calculatingunit; and a feeding pulse energy changing unit that changes theopen/close pattern set by the open/close pattern setting unit to theopen/close pattern in which a feeding pulse energy per feeding pulse ismade different between at a time of power feeding using the twoone-sides and at a time of power feeding using theupper-and-lower-both-side to reduce a difference between the machiningenergy calculated by the machining energy calculating unit and thereference machining energy.
 15. The wire electrical discharge machiningapparatus according to claim 1, wherein themachining-energy-distribution changing unit includes areference-machining-energy setting unit that sets a reference machiningenergy that provides a target value for the machining energy to becalculated by the machining energy calculating unit and provides amachining energy value that is different between an upper end side and alower end side of the machining gap; and a feeding pulse energy changingunit that changes the open/close pattern set by the open/close patternsetting unit to the open/close pattern in which a feeding pulse energyper feeding pulse is made different between at a time of power feedingusing the two one-sides and at a time of power feeding using theupper-and-lower-both-side to reduce a difference between the machiningenergy calculated by the machining energy calculating unit and thereference machining energy.